The present invention relates generally to the field of disc drive data storage devices and, more particularly, to an assembly of spindle motor and disc stack.
Disc drive data storage devices, known as "Winchester" type disc drives, are well known in the industry. In a Winchester disc drive, digital data are written to and read from a thin layer of magnetizable material on the surface of rotating discs. Write and read operations are performed through a transducer which is carried in a slider body. The slider and transducer are sometimes collectively referred to as a head, and typically a single head is associated with each disc surface. The heads are selectively moved under the control of electronic circuitry to any one of a plurality of circular, concentric data tracks on the disc surface by an actuator device. Each slider body includes a self-acting hydrodynamic air bearing surface. As the disc rotates, the disc drags air beneath the air bearing surface, which develops a lifting force that causes the slider to lift and fly several microinches above the disc surface.
In the current generation of disc drive products, the most commonly used type of actuator is a rotary moving coil actuator. The discs themselves are typically mounted in a "stack" on the hub structure of a brushless DC spindle motor. For example, the U.S. Pat. No. 5,089,922 issued to Steven P. LeClair and assigned to Seagate Technology, Inc., discloses a disc drive motor spindle hub for holding a disc and spacer stack firmly in place, the teachings of which are fully incorporated herein by reference. This patent teaches an improved disc flange design which accommodates for the bending of the disc flange, yet allowing for maximum clamp force to be applied to the disc stack away from the cylindrical hub.
The prior art disc flange and disc spacers are machined parts, with a roughness of the order of 30-40 microinches. The discs are typically made up of aluminum substrates and have a stamped circular inner hole to accommodate the spindle hub. Due to the stamping process, the disc surface in the vicinity of the inner hole will have uneven projections. Any residual distortion of the disc inside diameter that may exist after the stamping process can adversely affect the surface condition of the entire disc after clamping into a disc and spacer stack as that surface is forced down against another component like the disc flange or the disc spacers or clamp washer.
The disc spacers are typically made up of aluminum alloy and are continuously dinged, nicked and scratched due to handling after manufacture and prior to assembly in a disc and spacer stack. Similarly, the metallic clamp washers are also susceptible for handling damages prior to assembly.
As the flying height of the slider above the disc continues to come down, there is a need to minimize the inherent roughness of components that makeup a disc stack so that the heads can be safely flown across the disc surface while reducing the flying height.
There is also a need to minimize the impact of roughness imparted due to the stamping of the circular inner hole of the disc.
There is also a need to use a disc flange whose surface roughness is significantly less than 30-40 microinches and resists bending due to clamp force. There is also a need to apply majority of the clamping force away from the disc inner diameter.
There is also a need to use various components that make up a spindle motor and disc stack assembly like, hub flange, disc spacers and clamp washers whose surface roughness is significantly less than 30-40 microinches and whose change in surface roughness due to handling damages do not adversely impact the disc stack. Also, there is a need to consider alternate non-metallic materials like ceramic for these components while overcoming any adverse effects like electrostatic charge buildup.